This invention relates to an improved system for determining the x-ray exposure required for photography.
Medical diagnosis of internal human tissue is frequently performed by the use of motion picture x-ray techniques, particularly when the tissue of interest, such as, for example, the beating heart, is in motion. The technique involves use of an x-ray tube aimed at the patient, a fluorescent screen disposed on the opposite side of the patient, an image intensifier which views the fluorescent screen and increases the brightness of the image, and a motion picture film camera which records the moving image. A television system is often used to provide a display as the x-ray image is panned, so that the particular site of interest can be properly positioned while the motion picture film is being exposed.
Proper exposure of the motion picture film requires accurate information with respect to light content of the image which is to be photographed. This is presently obtained by extracting and directing at a photomultiplier exposure sensing system, a small sample of a portion of the light contained in a collimated beam formed from the visible image produced by the image intensifier. Since any part of the collimated beam is composed of light from all parts of the image, what is sensed is only an average sample which is representative of the total amount of light in the entire image. Since the image of the subject contains areas of both high and low x-ray absorptivity, it is difficult to determine accurately from a sample of the entire image the optimum exposure required for the particular body portion of interest which is only a part of that total image. Since, with the presently used system, the operator has no control over the location of the light sample taken, the result is often an unsatisfactory exposure.
The patient must then be subjected again to x-radiation in order to obtain a better picture. Since it is desirable to minimize exposure of the patient to x-radiation, it is advantageous and less potentially harmful to the patient to determine initially, the optimum exposure required for the particular body portion of interest.